Page 177 - Copper and Bronze in Art: Corrosion, Colorants, Getty Museum Conservation, By David Scott

environmental testing. A program of monitoring the thickness of the copper sheeting was
planned. Areas damaged by erosion corrosion or by water that had not been able to drain away
were patched with new sheets of copper. By current estimates, the original copper should last
for at least a thousand years.
The statue consists of three hundred panels fabricated with more than six hundred sheets
of copper, some panels made of more than one sheet, each sheet about 2.54 mm (0.1 inch) thick.
Parts of the statue's tablet and the crown rays have the visual appearance of yellow brass. His­
torical photographs taken in 1965,1974, and 1983 show that since 1965, large areas on the left side
of the statue, facing toward Manhattan, have darkened. Eddy-current measurements showed
the thickness of the patina in these darker areas to be 0.1-0.5 of the thickness of the patina in
adjacent green areas; wind erosion, aqueous runoff, or both are possible causes.
The overall green patina of the statue is predominantly brochantite, while the green patina
on the darkened areas has a high antlerite content. Analysis of the patina on a piece of cop­
per removed from the statue in 1905 showed no antlerite content, so there may have been an
environmental change in recent decades to produce the antlerite corrosion crust in places. The
brass components in the tablet and crown show varying degrees of localized corrosion, includ­
ing black deposits and pitting as well as green patina formation, since brass weathers more
severely than copper.

The Great Buddha Many exposed bronzes present a complex picture when exam-
at Kamakura ined in detail. Matsuda and Aoki (1996) carried out such a study
of the patina on the Great Buddha at the Kotoku-in temple in
Kamakura, Japan. This impressive hollow bronze, shown in PLATE 37, was made in 1252; it
is 13.35 m high and weighs 120 tons. The statue was cast in sections from separate pours with
a variety of joins between the sections rather than simple butt joins. The alloy is 69% copper,
9% tin, 20% lead, 0.04% iron, and 0.08% aluminum (Sekino 1965; Toishi 1965; Maruyasu and
Oshima 1965).
The formation of the principal patina components was influenced by the localized environ­
ment affecting different regions of the sculpture. The initial patina contains cuprite, which is
generally covered with brochantite. Malachite was also detected with the brochantite, suggest­
ing that a malachite patina originally formed and was partially transformed into brochantite by
more recent environmental pollution, including increased sulfur dioxide in the atmosphere.
Antlerite was detected on the back and west-facing sides of the Buddha, while atacamite was
dominant in the south-facing patina.
Besides brochantite, which is the primary component, an unusually wide array of other
minerals were also detected in the patina, some of which are listed in TABLE 5.3. A lead chloro-
phosphate, Pb 5 (P0 4 ) 3 Cl, was found on the front on the statue. Lead sulfate (anglesite), PbS0 4 ,
was identified on the back along with a basic lead phosphate, Pb 5 (P0 4 ) 3 OH.

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